The following descriptions and examples are not admitted to be prior art by virtue of their inclusion in this section.
Acoustic waves in fluid-filled boreholes may be excited and recorded from sonic logging tools. Their propagation in the borehole is affected by the type of surrounding rocks. More specifically, non-dispersive acoustic waves have been observed such as P- and S-headwaves, and dispersive waves such as Stoneley and pseudo-Rayleigh waves in monopole logging and flexural waves in dipole logging. In contrast to the constant slowness at all frequencies for the non-dispersive modes, the dispersive waves exhibit varied phase and group slownesses at different frequencies. Analysis and estimation of the slowness and its change over the frequency (i.e., the dispersion) provide important information to infer the properties of surrounding formation. For example, the compressional and shear slownesses have been used for reservoir characterizations and radial profiling of near-wellbore formation.